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Abstract

We demonstrate that semiconductor nanowires can be translated, rotated, cut, fused and organized into nontrivial structures using holographic optical traps. The holographic approach to nano-assembly allows for simultaneous independent manipulation of multiple nanowires, including relative translation and relative rotation.

Figures (5)

Holographically trapping semiconductor nanowires. (a) The light from a frequency-doubled solid-state laser is imprinted with a computer-generated hologram by a phase-shifting spatial light modulator (SLM) before being relayed to the input pupil of a high-numerical-aperture objective lens, which focuses the light into an array of optical traps, shown in (b). (c) An individual semiconductor nanowire can be localized by multiple optical traps, whose intersection with the wire typically is visualized by intense laser-induced fluorescence, as in (d).

Translation and rotation of semiconductor nanowires by holographic trap arrays. (a) Two free-floating semiconductor nanowires translated toward each other with parallel arrays of holographic optical traps. One wire is held stationary in one line of traps while the other is translated by moving a second line of traps in discrete steps of 700 nm. The traps in each line are separated by 0.4 μm and each trap is powered by 3 mW. (b) Rotating a semiconductor nanowire by rotating an array of traps in discrete steps of 5°. The optically trapped CdS nanowires in these sequences appear bright because of photoluminescence excited by the strongly focused optical traps. Because these images are created with a filter that blocks the bandgap emission of CdS [16], the luminescence can be attributed to emission from defect sites in the CdS material [17].

Rotating a semiconductor nanowire with the orbital angular momentum flux of a helical mode of light. (a) When transmitted to the SLM, the helical phase mask φ(r,θ) =ℓθ transforms the wavefronts of a TEM00 laser mode into an ℓ-fold helix. This helical beam focuses into the ring-like optical trap, shown in (b). The orbital angular momentum density in this trap can be used to rotate a semiconductor nanowire, as shown in the sequence of photographs in (c), which are separated by 1 sec intervals. The dashed circle shows the position of an ℓ = 30 optical vortex at 1 W.

Transforming nanowires with intense focused beams of light. (a) Cutting a semiconductor nanowire with an optical scalpel. A bent nanowire is brought to the focus of an optical trap powered by 0.5 W. An exposure time of 100 ms results in a clean cut at the bend. (b) Fusing two semiconductor nanowires into a free-floating assembly. The two nanowires are first trapped and then manipulated to form a T-junction. An optical trap powered by 100 mW is then focused on the junction for 1 s to non-destructively fuse the wires. The T-junction then floats freely once the traps are extinguished.

Assembly of rhombus constructed from semiconductor nanowires using holographic optical traps. (a) A nanowire is translated towards an existing structure created earlier by trapping and fusing two nanowires. (b) The long nanowire is then cut with a pulsed optical scalpel. (c) The resulting free-floating nanowire piece then is brought back to the partially completed structure. (d) The free-floating structure is completed by fusing both ends of the fourth nanowire.